一、前言

        接下来是开展一系列的 SpringCloud 的学习之旅，从传统的模块之间调用，一步步的升级为 SpringCloud 模块之间的调用，此篇文章为第十六篇，即使用 Sentinel 实现熔断功能。

二、 Ribbon 系列

        首先我们新建两个服务的提供者模块 cloudalibaba-provider-payment9003 和 cloudalibaba-provider-payment9004，这两个模块除了配置文件里面的端口号和主启动类不一样，其他的都一样，我这里只介绍其中一个模块的创建过程，pom.xml 内容如下：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><parent><groupId>com.springcloud</groupId><artifactId>SpringCloud</artifactId><version>1.0-SNAPSHOT</version></parent><artifactId>cloudalibaba-provider-payment9003</artifactId><properties><maven.compiler.source>8</maven.compiler.source><maven.compiler.target>8</maven.compiler.target><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><dependencies><!--SpringCloud ailibaba nacos --><dependency><groupId>com.alibaba.cloud</groupId><artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId></dependency><dependency><!-- 引入自己定义的api通用包，可以使用Payment支付Entity --><groupId>com.springcloud</groupId><artifactId>cloud-api-commons</artifactId><version>${project.version}</version></dependency><!-- SpringBoot整合Web组件 --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-actuator</artifactId></dependency><!--日常通用jar包配置--><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-devtools</artifactId><scope>runtime</scope><optional>true</optional></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency></dependencies>
</project>

        application.yml 内容如下所示：

server:port: 9003spring:application:name: nacos-payment-providercloud:nacos:discovery:server-addr: localhost:8848 #配置Nacos地址management:endpoints:web:exposure:include: '*'

        主启动类代码如下：

package com.springcloud;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;@SpringBootApplication
@EnableDiscoveryClient
public class PaymentMain9003
{public static void main(String[] args) {SpringApplication.run(PaymentMain9003.class, args);}
}

        对外提供的 controller 代码如下：

package com.springcloud.controller;import com.springcloud.entities.CommonResult;
import com.springcloud.entities.Payment;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;import java.util.HashMap;@RestController
public class PaymentController {@Value("${server.port}")private String serverPort;public static HashMap<Long, Payment> hashMap = new HashMap<>();static{hashMap.put(1L,new Payment(1L,"28a8c1e3bc2742d8848569891fb42181"));hashMap.put(2L,new Payment(2L,"bba8c1e3bc2742d8848569891ac32182"));hashMap.put(3L,new Payment(3L,"6ua8c1e3bc2742d8848569891xt92183"));}@GetMapping(value = "/paymentSQL/{id}")public CommonResult<Payment> paymentSQL(@PathVariable("id") Long id){Payment payment = hashMap.get(id);CommonResult<Payment> result = new CommonResult(200,"from mysql,serverPort:  "+serverPort,payment);return result;}
}

        创建一个服务的消费者模块 cloudalibaba-consumer-nacos-order84，pom.xml 内容如下所示：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><parent><groupId>com.springcloud</groupId><artifactId>SpringCloud</artifactId><version>1.0-SNAPSHOT</version></parent><artifactId>cloudalibaba-consumer-nacos-order84</artifactId><properties><maven.compiler.source>8</maven.compiler.source><maven.compiler.target>8</maven.compiler.target><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><dependencies><!--SpringCloud openfeign --><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-openfeign</artifactId></dependency><!--SpringCloud ailibaba nacos --><dependency><groupId>com.alibaba.cloud</groupId><artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId></dependency><!--SpringCloud ailibaba sentinel --><dependency><groupId>com.alibaba.cloud</groupId><artifactId>spring-cloud-starter-alibaba-sentinel</artifactId></dependency><!-- 引入自己定义的api通用包，可以使用Payment支付Entity --><dependency><groupId>com.springcloud</groupId><artifactId>cloud-api-commons</artifactId><version>${project.version}</version></dependency><!-- SpringBoot整合Web组件 --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-actuator</artifactId></dependency><!--日常通用jar包配置--><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-devtools</artifactId><scope>runtime</scope><optional>true</optional></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency></dependencies>
</project>

        application.yml 代码如下所示：

server:port: 84spring:application:name: nacos-order-consumercloud:nacos:discovery:server-addr: localhost:8848sentinel:transport:#配置Sentinel dashboard地址dashboard: localhost:8080#默认8719端口，假如被占用会自动从8719开始依次+1扫描,直至找到未被占用的端口port: 8719#消费者将要去访问的微服务名称(注册成功进nacos的微服务提供者)
service-url:nacos-user-service: http://nacos-payment-provider# 激活Sentinel对Feign的支持
feign:sentinel:enabled: true

        主启动类代码如下：

package com.springcloud;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.openfeign.EnableFeignClients;@EnableDiscoveryClient
@SpringBootApplication
@EnableFeignClients
public class OrderNacosMain84
{public static void main(String[] args) {SpringApplication.run(OrderNacosMain84.class, args);}
}

        配置类代码如下，使其支持负载均衡

package com.springcloud.config;import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.client.RestTemplate;@Configuration
public class ApplicationContextConfig
{@Bean@LoadBalancedpublic RestTemplate getRestTemplate(){return new RestTemplate();}
}

        业务类 controller 代码如下：

@Slf4j
@RestController
public class CircleBreakerController {public static final String SERVICE_URL = "http://nacos-payment-provider";@Resourceprivate RestTemplate restTemplate;@RequestMapping("/consumer/fallback/{id}")@SentinelResource(value = "fallback") //没有配置public CommonResult<Payment> fallback(@PathVariable Long id){CommonResult<Payment> result = restTemplate.getForObject(SERVICE_URL + "/paymentSQL/"+id,CommonResult.class,id);if (id == 4) {throw new IllegalArgumentException ("IllegalArgumentException,非法参数异常....");}else if (result.getData() == null) {throw new NullPointerException ("NullPointerException,该ID没有对应记录,空指针异常");}return result;}
}

        分别启动两个服务提供者和一个消费者，启动完成后，访问 http://localhost:84/consumer/fallback/1，进行测试，多刷新几次，可以看到，服务之间的调用没有任何问题，且负载均衡好用。

        当我们访问第四条和第五条数据时，由于我们人为的配置了抛出异常，给用户展示了 error 的界面，效果并不是很好，如下图：

2.1 只配置 fallback

        为了解决上面返回给客户不友好的界面，我们可以配置 fallback 属性来解决这个问题，它可以对业务的异常进行兜底，修改 CircleBreakerController 类，加上 fallback 属性和其对应的方法，如下：

@Slf4j
@RestController
public class CircleBreakerController {public static final String SERVICE_URL = "http://nacos-payment-provider";@Resourceprivate RestTemplate restTemplate;@RequestMapping("/consumer/fallback/{id}")// @SentinelResource(value = "fallback") //没有配置@SentinelResource(value = "fallback", fallback = "handlerFallback") // fallback 只负责业务异常public CommonResult<Payment> fallback(@PathVariable Long id) {CommonResult<Payment> result = restTemplate.getForObject(SERVICE_URL + "/paymentSQL/" + id, CommonResult.class, id);if (id == 4) {throw new IllegalArgumentException("IllegalArgumentException,非法参数异常....");} else if (result.getData() == null) {throw new NullPointerException("NullPointerException,该ID没有对应记录,空指针异常");}return result;}public CommonResult handlerFallback(@PathVariable Long id, Throwable e) {Payment payment = new Payment(id, "null");return new CommonResult<>(444, "兜底异常handlerFallback,exception内容  " + e.getMessage(), payment);}
}

        重启模块，当我们再次访问第四条和第五条数据时，效果就很好了，如下图：

2.2 只配置 blockHandler

        修改 CircleBreakerController 类，加上 blockHandler 属性和其对应的方法，如下：

@Slf4j
@RestController
public class CircleBreakerController {public static final String SERVICE_URL = "http://nacos-payment-provider";@Resourceprivate RestTemplate restTemplate;@RequestMapping("/consumer/fallback/{id}")// @SentinelResource(value = "fallback") //没有配置// @SentinelResource(value = "fallback", fallback = "handlerFallback") // fallback 只负责业务异常@SentinelResource(value = "fallback",blockHandler = "blockHandler") //blockHandler 只负责sentinel控制台配置违规public CommonResult<Payment> fallback(@PathVariable Long id) {CommonResult<Payment> result = restTemplate.getForObject(SERVICE_URL + "/paymentSQL/" + id, CommonResult.class, id);if (id == 4) {throw new IllegalArgumentException("IllegalArgumentException,非法参数异常....");} else if (result.getData() == null) {throw new NullPointerException("NullPointerException,该ID没有对应记录,空指针异常");}return result;}public CommonResult blockHandler(@PathVariable  Long id, BlockException blockException) {Payment payment = new Payment(id,"null");return new CommonResult<>(445,"blockHandler-sentinel限流,无此流水: blockException  "+blockException.getMessage(),payment);}
}

        配置完毕后打开 sentinel 的管理界面配置降级规则，如下：

        在浏览器访问 http://localhost:84/consumer/fallback/4，如果点击一次，返回的还是 java 的运行时异常信息，如下图：

        如果多点击几次，则显示的是 blockHandler 指定的返回信息，如下图：

2.3 配置 fallback 和 blockHandler

        若既配置了 fallback，又配置了 blockHandler，又会出现什么效果呢？修改 CircleBreakerController 类，代码如下：

@Slf4j
@RestController
public class CircleBreakerController {public static final String SERVICE_URL = "http://nacos-payment-provider";@Resourceprivate RestTemplate restTemplate;@RequestMapping("/consumer/fallback/{id}")// @SentinelResource(value = "fallback") //没有配置// @SentinelResource(value = "fallback", fallback = "handlerFallback") // fallback 只负责业务异常// @SentinelResource(value = "fallback",blockHandler = "blockHandler") //blockHandler 只负责sentinel控制台配置违规@SentinelResource(value = "fallback",fallback = "handlerFallback",blockHandler = "blockHandler")public CommonResult<Payment> fallback(@PathVariable Long id) {CommonResult<Payment> result = restTemplate.getForObject(SERVICE_URL + "/paymentSQL/" + id, CommonResult.class, id);if (id == 4) {throw new IllegalArgumentException("IllegalArgumentException,非法参数异常....");} else if (result.getData() == null) {throw new NullPointerException("NullPointerException,该ID没有对应记录,空指针异常");}return result;}// 本例是 fallbackpublic CommonResult handlerFallback(@PathVariable  Long id,Throwable e) {Payment payment = new Payment(id,"null");return new CommonResult<>(444,"兜底异常handlerFallback,exception内容  "+e.getMessage(),payment);}// 本例是 blockHandlerpublic CommonResult blockHandler(@PathVariable  Long id,BlockException blockException) {Payment payment = new Payment(id,"null");return new CommonResult<>(445,"blockHandler-sentinel限流,无此流水: blockException  "+blockException.getMessage(),payment);}
}

        在 sentinel 中配置一个限流规则，如下：

        在浏览器访问 http://localhost:84/consumer/fallback/1，如果点击一次，返回结果如下：

         频繁点击，效果如下，可以看到限流效果出现了。

        在浏览器访问 http://localhost:84/consumer/fallback/4，点击一次，返回结果如下，是 fallback 生效了。 

         频繁点击，效果如下，可以看到限流效果出现了。

2.4 结论

        若 blockHandler 和 fallback 都进行了配置，则被限流降级而抛出 BlockException 时只会进入 blockHandler 处理逻辑。

2.5 忽略属性

        假如我有一个异常，我不想让 fallback 方法帮我兜底，我就可以通过配置 exceptionsToIgnore 属性来实现，修改 CircleBreakerController 类的代码，添加 exceptionsToIgnore 属性，如下：

@Slf4j
@RestController
public class CircleBreakerController {public static final String SERVICE_URL = "http://nacos-payment-provider";@Resourceprivate RestTemplate restTemplate;@RequestMapping("/consumer/fallback/{id}")// @SentinelResource(value = "fallback") //没有配置// @SentinelResource(value = "fallback", fallback = "handlerFallback") // fallback 只负责业务异常// @SentinelResource(value = "fallback",blockHandler = "blockHandler") //blockHandler 只负责sentinel控制台配置违规@SentinelResource(value = "fallback",fallback = "handlerFallback",blockHandler = "blockHandler",exceptionsToIgnore = {IllegalArgumentException.class})public CommonResult<Payment> fallback(@PathVariable Long id) {CommonResult<Payment> result = restTemplate.getForObject(SERVICE_URL + "/paymentSQL/" + id, CommonResult.class, id);if (id == 4) {throw new IllegalArgumentException("IllegalArgumentException,非法参数异常....");} else if (result.getData() == null) {throw new NullPointerException("NullPointerException,该ID没有对应记录,空指针异常");}return result;}// 本例是 fallbackpublic CommonResult handlerFallback(@PathVariable  Long id,Throwable e) {Payment payment = new Payment(id,"null");return new CommonResult<>(444,"兜底异常handlerFallback,exception内容  "+e.getMessage(),payment);}// 本例是 blockHandlerpublic CommonResult blockHandler(@PathVariable  Long id,BlockException blockException) {Payment payment = new Payment(id,"null");return new CommonResult<>(445,"blockHandler-sentinel限流,无此流水: blockException  "+blockException.getMessage(),payment);}
}

        在 sentinel 中配置降级规则，如下图：

        在浏览器中访问 http://localhost:84/consumer/fallback/4，如下图，可以发现，fallback 方法并没有生效，但是限流方法方法生效了

三、Feign 系列

3.1 maven 依赖

        首先确保消费者模块 cloudalibaba-consumer-nacos-order84 的 pom.xml 中引入了 openFegin 的依赖，如下：

<!--SpringCloud openfeign -->
<dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>

3.2 修改配置文件

        接下来需要在 application.yml 中激活 sentinel 对 Feign 的支持，如下：

3.3 相关业务类

        编写带有 @FeignClient 注解的业务接口，如下：

package com.springcloud.service;import com.springcloud.entities.CommonResult;
import com.springcloud.entities.Payment;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;@FeignClient(value = "nacos-payment-provider",fallback = PaymentFallbackService.class)
public interface PaymentService
{@GetMapping(value = "/paymentSQL/{id}")public CommonResult<Payment> paymentSQL(@PathVariable("id") Long id);
}

        然后编写 fallback 参数指定的的兜底方法的类，代码如下：

package com.springcloud.service;import com.springcloud.entities.CommonResult;
import com.springcloud.entities.Payment;
import org.springframework.stereotype.Component;@Component
public class PaymentFallbackService implements PaymentService
{@Overridepublic CommonResult<Payment> paymentSQL(Long id){return new CommonResult<>(44444,"服务降级返回,---PaymentFallbackService",new Payment(id,"errorSerial"));}
}

        修改 CircleBreakerController 类，在里面添加如下的方法：

    @Resourceprivate PaymentService paymentService;@GetMapping(value = "/consumer/paymentSQL/{id}")public CommonResult<Payment> paymentSQL(@PathVariable("id") Long id){return paymentService.paymentSQL(id);}

        不要忘了在启动类上添加启用 Feign 的注解，如下图：

3.4 测试

        分别启动 cloudalibaba-provider-payment9003 模块和 cloudalibaba-consumer-nacos-order84 模块，在浏览器输入：http://localhost:84/consumer/paymentSQL/1，如下图，可以正常的访问：

         此时故意关闭 9003 微服务提供者，看 84 消费侧自动降级，会不会被耗死，如下图，可以看到，自动进入到了我们指定的兜底方法里面了。

四、熔断框架比较